Zoom lens system, and image pickup system using the same

ABSTRACT

The invention provides a zoom lens system much more reduced in size and cost than ever before and best-suited for use on portable information terminals of small size. The zoom lens system comprises, in order from an object side thereof, a first lens group G 1  having positive refracting power and designed to be fixed during zooming, a second lens group G 2  having negative refracting power and designed to move from the object side to an image plane side of the system for zooming from a wide-angle end to a telephoto end of the system, a third lens group having refracting power and designed to move from the image plane side to the object side for zooming from the wide-angle end to the telephoto end, and a fourth lens group G 4  having positive refracting power and designed to be movable during zooming. Condition (1) with respect to the power of the third lens group G 3,  condition (2) with respect to the amount of zooming movement of the third lens group G 3  or condition (3) with respect to the composite power of the third and fourth lens groups G 3  and G 4  and condition (10) with respect to the actual value of the back focus are satisfied.

[0001] This application claims benefit of Japanese Application(s) No.Hei 11-316827 filed in Japan on Nov. 8, 1999, the contents of which areincorporated by this reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a zoom lens system andan image pickup system using the same, and more particularly to acompact yet low-cost zoom lens system for cameras using an electronicimage pickup means, for instance, camcorders, digital cameras,surveillance monitor cameras and cameras incorporated in portabletelephones or PCs.

SUMMARY OF THE INVENTION

[0003] For zoom lens systems which belong to this field and are reducedin size and cost for consumer-oriented purposes, there has been proposeda four-group zoom lens system of +−++ construction in order from itsobject side, as shown in JP-A's 4-43311 and 4-78806. In this zoom lenssystem, the first and third lens groups are fixed during zooming, andthe second lens group having negative power moves on an optical axis forzooming while the fourth lens group moves on the optical axis forcorrection of fluctuations of an image plane position with zooming. Inzoom lens systems as set forth in JP-A's 6-94997 and 6-194572, on theother hand, the third lens group is moved from the image plane side tothe object side for zooming from the wide-angle end to the telephoto endfor the purpose of aiding in zoom action, thereby achieving further sizereductions. These publications show zoom lenses having a relatively highzoom ratio of the order of 8 to 12. For a zoom lens system reducedexclusively in size and cost at the expense of zoom ratios, however,such prior art systems are still less than satisfactory because nosufficient size reductions are achievable thanks to an increased numberof lenses.

[0004] In the zoom lenses shown in the aforesaid JP-A's 6-94997 and6-194572, a substantial portion of their zooming action is assigned tothe second lens group. To keep a substantially constant image point inthis case, the transverse magnification of the second lens group must bein the neighborhood of −1 in the range from the wide-angle end to thetelephoto end of the system. When further size reductions are intendedby making the zoom ratio smaller than this, however, the amount ofmovement of the second lens group can be so reduced that the spacemargin between the first and second lens groups can be cut to the bone,thereby achieving efficient size reductions.

[0005] To perform zooming while the second lens group has a transversemagnification in the neighborhood of −1 with a narrower spacing betweenthe first and second lens groups, however, it is required to increasethe power of the first lens group with respect to the second lens group.This in turn causes an entrance pupil to be located at a fartherposition and so the height of off-axis rays passing through the firstlens group to increase, resulting unavoidably in an increase in the sizeand, hence, the thickness of the first lens group. It is also requiredto increase the curvature of each lens in the first lens group. Toensure each lens of sufficient edge thickness, it is then necessary toincrease the thickness of each lens in the first lens group.

SUMMARY OF THE INVENTION

[0006] In view of such states of the prior art as explained above, anobject of the present invention is to provide a zoom lens system muchmore reduced in size and cost than ever before, and an image pickupsystem using the same.

[0007] One specific object of the present invention is to provide afour-group zoom lens system which can have the desired zoom ratio whileits size is reduced without increasing the power ratio of the first lensgroup with respect to the second lens group.

[0008] Another specific object of the present invention is to achieve acompact zoom lens system suitable for use on digital cameras, andcameras added to portable telephones and PCs, which is designed in sucha way as to provide a nearly telecentric exit beam with image pickupdevices such as CCDs and CMOSs in mind. This zoom lens system ensuresthe desired back focus enough to receive a low-pass filter, a beamsplitter, etc. if required, and achieves improved image-formationcapability with a reduced number of lenses.

[0009] According to one aspect of the present invention, these objectsare achievable by the provision of a zoom lens system characterized bycomprising, in order from an object side of the zoom lens system, afirst lens group having positive refracting power and designed to befixed during zooming, a second lens group having negative refractingpower and designed to move from the object side to an image plane sideof the zoom lens system for zooming from a wide-angle end to a telephotoend of the zoom lens system, a third lens group having positiverefracting power and designed to move from the image plane side to theobject side for zooming from the wide-angle end to the telephoto end,and a fourth lens group having positive refracting power and designed tobe movable for zooming, wherein the following conditions are satisfied:

0.5<|F ₂ /F ₃|<1.2  (1)

2.5 mm<f _(B(min))<4.8 mm  (10)

[0010] where F_(i) is the focal length of an i-th lens group andf_(B(min)) is the length, as calculated on an air basis, of the finalsurface of a lens having power in said zoom lens system to an imageplane of said zoom lens system, representing a figure at which said zoomlens system becomes shortest in a whole zooming space.

[0011] According to another aspect of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of the zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of the zoom lens system forzooming from a wide-angle end to a telephoto end of the zoom lenssystem, a third lens group having positive refracting power and designedto move from the image plane side to the object side for zooming fromthe wide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied:

0.49<|L ₃ /L ₂|<1  (2)

2.5 mm<f _(B(min))<4.8 mm  (10)

[0012] where L_(i) is the amount of movement of an i-th lens group fromthe wide-angle end to the telephoto end and f_(B(min)) is the length, ascalculated on an air basis, of the final surface of a lens having powerin said zoom lens system to an image plane of said zoom lens system,representing a figure at which said zoom lens system becomes shortest ina whole zooming space.

[0013] According to yet another aspect of the present invention, thereis provided a zoom lens system characterized by comprising, in orderfrom an object side of the zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of the zoom lens system forzooming from a wide-angle end to a telephoto end of the zoom lenssystem, a third lens group having positive refracting power and designedto move from the object side to the image plane side for zooming fromthe wide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied:

2<(F _(3.4W))/IH<3.3  (3)

2.5 mm<f _(B(min))<4.8 mm  (10)

[0014] where (F_(3.4W)) is the composite focal length of the third andforth lens groups at the wide-angle end, IH is the radius of an imagecircle, and f_(B(min)) is the length, as calculated on an air basis, ofthe final surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.

[0015] According to a further aspect of the present invention, there isprovided a zoom lens system, characterized by comprising, in order froman object side of the zoom lens system, a first lens group havingpositive refracting power, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming a wide-angle end to atelephoto end of the zoom lens system, a third lens group havingpositive refracting power and a fourth lens group having positiverefracting power and designed to be movable for zooming, wherein saidthird lens group comprises, in order from an object side thereof, apositive lens component convex on an object side thereof and a cementedlens consisting of a positive lens element convex on an object sidethereof and a negative lens element concave on an image plane sidethereof, and both the object-side positive lens component and cementedlens in said third lens group are held in a lens barrel while theobject-side convex surfaces thereof abut at their peripheries or theirperipheral spots against said lens barrel, wherein the followingcondition is satisfied:

2.5 mm<f _(B(min))<4.8 mm  (10)

[0016] where f_(B(min)) is the length, as calculated on an air basis, ofthe final surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.

[0017] Why the aforesaid lens arrangements are herein used and how theywork are now explained.

[0018] In recent fields of camcorders and digital cameras as well asinformation systems using image pickup devices, e.g., portabletelephones and personal computers, too, there are growing demands forconsumer-oriented compact yet low-cost zoom lenses. Zoom lenses capableof meeting such demands, for instance, are disclosed in JP-A's 6-94997and 6-194572 already referred to herein. As already explained, each zoomlens system has a zoom ratio of about 8 to 12, with a substantialportion of its zooming function allocated to the second lens group. Tokeep a substantially constant image point in this case, the transversemagnification of the second lens group must be in the neighborhood of −1in the range from the wide-angle end to the telephoto end of the system.

[0019] When further size reductions are intended by making the zoomratio smaller than this, however, the amount of movement of the secondlens group can be so reduced that the space margin between the first andsecond lens groups can be cut to the bone, thereby achieving efficientsize reductions.

[0020] To perform zooming while the second lens group has a transversemagnification in the neighborhood of −1 with a narrower spacing betweenthe first and second lens groups, however, it is required to increasethe power of the first lens group with respect to the second lens group.This in turn causes an entrance pupil to be located at a fartherposition and so the height of off-axis rays passing through the firstlens group to increase, resulting unavoidably in an increase in the sizeand, hence, the thickness of the first lens group. It is also requiredto increase the curvature of each lens in the first lens group. Toensure each lens of sufficient edge thickness, it is then necessary toincrease the thickness of each lens in the first lens group.

[0021] According to the present invention, these problems can be avertedby increasing the proportion of the zooming action allocated to thethird lens group, thereby ensuring the desired zoom ratio with nosignificant variation in the power ratio between the first lens groupand the second lens group and, hence, achieving size reductions. Toallow the third lens group to have such an increased zooming action, itis required to have relatively large power, as defined by condition (1).When the lower limit of 0.5 to condition (1) is not reached or when thepower of the third lens group becomes weak with respect to the power ofthe second lens group, no size reductions are achievable because theamount of zooming movement of the third lens group becomes too largeand, accordingly, the amount of movement of the second lens group tokeep the image plane at a constant position becomes large. When theupper limit of 1.2 to condition (1) is exceeded or when the power of thethird lens group becomes strong with respect to the power of the secondlens group, the amount of astigmatism produced at the third lens groupbecomes too large, and no sufficient space can be obtained between thesecond and third lens groups because the distance between the third lensgroup and an object point with respect thereto becomes too short. Toinsert an image pickup package such as CCDs and CMOSs as well as an IRcut filter, a low-pass filter or the like in the optical system, it isthen required that the back focus f_(B) be 2.5 mm or greater. When theback focus f_(B) exceeds 4.8 mm, on the other hand, no compactness canbe achieved. For this reason, it is required that the followingcondition (10) be satisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

[0022] where f_(B(min)) is the length, as calculated on an air basis, ofthe final surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space. By theterm “lens having power” is herein intended a lens whose refractingpower is not zero.

[0023] When the lower limit of 2.5 mm to condition (1) is not reached,it is impossible to obtain any space for receiving filters such as an IRcut filter. When the upper limit of 4.5 mm is exceeded, on the otherhand, the size of the zoom lens system increases. This condition isparticularly important for reducing the size of an optical system usedwith an image pickup device for portable telephones or notebook PCs.

[0024] More preferably, the zoom lens system of the invention shouldsatisfy the following condition (4):

0.6<|F ₂ /F ₃|<1  (4)

[0025] To allow the third lens group to have a relatively large zoomingaction as mentioned above, it is required to increase the amount ofzooming movement of the third lens group, as defined by condition (2)giving a definition of the ratio of the amount of movement from thewide-angle end to the telephoto end between the second lens group andthe third lens group. When the lower limit of 0.49 to condition (2) isnot reached or when the amount of movement of the third lens groupbecomes small with respect to the second lens group, it is impossible toallocate any sufficient zooming action to the third lens group. When theupper limit of 1 is exceeded or when the amount of movement of the thirdlens group becomes large with respect to the second lens group,fluctuations of aberrations such as astigmatism and coma become toolarge during zooming with the third lens group, and no sufficient spacecan be obtained between the second lens group and the third lens group,because the distance at the telephoto end between the third lens groupand the object point with respect thereto becomes too short.

[0026] To reduce the overall length of such a four-group zoom lenssystem of +−++ construction as intended herein, it is effective to makestrong the powers of the third and fourth lens groups for relaying avirtual image formed by the first and second lens group to the imagepickup plane, thereby reducing the distance from the position of thevirtual image formed by the first and second lens groups to the imagepickup plane. It is thus preferable to make the composite power of thethird and fourth lens groups strong, as defined by condition (3). Whenthe upper limit of 3.3 to condition 3 is exceeded or when the compositefocal length of the third and fourth lens groups at the wide-angle endbecomes long with respect to the image circle radius (image height) IH(the power becomes weak), no sufficient size reductions are achievablefor the foregoing reasons. When the lower limit of 2 to condition (3) isnot reached or when the composite focal length of the third and fourthlens groups at the wide-angle end becomes short with respect to theimage circle radius (the power becomes strong), astigmatisms produced atthe third and fourth lens groups become too large, and no sufficientspace can be obtained between the second and third lens groups at thetelephoto end, because the distance between the third lens group and theobject point with respect thereto becomes too short.

[0027] For such a zoom lens system as intended herein, it is preferableto carry out focusing with the fourth lens group wherein the angle ofincidence of an axial light beam is relatively small, because aberrationfluctuations with focusing can be limited. In addition, the fourth lensgroup, because of being relatively small in lens diameter and light inweight, has the merit of reducing the driving torque for focusing.

[0028] To reduce the overall length of the zoom lens system, the largestpossible portion of the composite power of the third and fourth lensgroups should preferably be allocated to the third lens group. In thepresent invention, the power of the third lens group is thus relativelylarger than that of the fourth lens group, as defined by the followingcondition (5) giving a definition of the ratio of the focal length ofthe third lens group with respect to that of the fourth lens group.

0.3<F ₃ /F ₄<0.8  (5)

[0029] Here F_(i) is the focal length of an i-th lens group. By makingthe focal length ratio of the third lens group with respect to thefourth lens group lower than the upper limit of 0.8 to condition (5), itis possible to achieve more considerable size reductions than everbefore. When the focal length ratio of the third lens group with respectto the fourth lens group is below the lower limit of 0.3 to condition 5,however, the power of the fourth lens group becomes too weak or theamount of focusing movement of the fourth lens group becomes too large,resulting in increased aberration fluctuations with focusing.

[0030] To reduce the size of the zoom lens system according to thepresent invention, the fourth lens group should preferably comprise onepositive lens. This is because the power of the fourth lens group isrelatively smaller than that of the third lens group, as mentionedabove.

[0031] To reduce astigmatism fluctuations with zooming, at least onesurface in the fourth lens group should preferably be defined by anaspherical surface.

[0032] Preferably, the zoom lens system of the present invention shouldsatisfy the following condition (6):

0.4<|β_(2T)|<1  (6)

[0033] Here β_(2T) is the transverse magnification of the second lensgroup at the telephoto end of the zoom lens system.

[0034] Condition (6) gives a definition of the absolute value of thetransverse magnification of the second lens group at the telephoto endof the zoom lens system. When the absolute value of the transversemagnification of the second lens group at the telephoto end is below thelower limit of 0.4, the zooming action of the second lens group becomesinsufficient and the power of the first lens group becomes too weak toachieve lens size reductions. On the other hand, when the absolute valueof the transverse magnification of the second lens group at thetelephoto end exceeds the upper limit of 1, the zooming action of thethird lens group becomes insufficient and the power of the first lensgroup becomes too strong, resulting in an increase in the lens diameterof the first lens group and failing to achieve size reductions.

[0035] To reduce the overall size of the zoom lens system, the thirdlens group should preferably have an increased power with no change inits image-formation magnification. Preferably in this case, theprincipal points of the third lens group should be positioned as closeto the object side as possible, thereby preventing the interference ofthe second lens group with the third lens group at the telephoto end,which may otherwise be caused by a reduction in the distance between thethird lens group and the object point with respect to the third lensgroup. Thus, the third lens group should comprise three lenses or apositive, a positive and a negative lens in order from the object side,with at least one aspherical surface provided for correction ofspherical aberrations.

[0036] If at least one surface in the second lens group is defined by anaspherical surface, it is then possible to make much better correctionfor fluctuations of astigmatism and coma with zooming.

[0037] In the present invention, the relatively large zooming action isassigned to the third lens group as mentioned above, so that loads ofcorrection of aberrations on the first and second lens groups can berelieved. For this reason, the first lens group can be comprised of onepositive lens. To make correction for chromatic aberration ofmagnification produced at the first lens group, the lens located nearestto the object side in the second lens group should preferably becomposed of a negative lens having relatively large dispersion, asdefined by the following condition (7) giving a definition of the Abbe'snumber of the negative lens located nearest to the object side in thesecond lens group.

ν₂₁<40  (7)

[0038] Here ν₂₁ is the Abbe's number of the negative lens locatednearest to the object side in the second lens group.

[0039] To make correction for the chromatic aberration of magnificationproduced at the first lens group or the positive lens, it is preferablethat the Abbe's number of the negative lens located nearest to theobject side in the second lens group does not exceed the upper limit of40 to condition (7). If the following condition (8) is satisfied, it isthen possible to make much better correction for the chromaticaberration of magnification.

ν₂₁<35  (8)

[0040] When the third lens group is made up of three lenses or apositive, a positive and a negative lens in order from the object sideas contemplated herein, two positive lenses should be each convex on anobject side thereof and one negative lens should have a strong concavesurface on an image plane side thereof. This is because the principalpoints of the third lens groups should be located as close to the objectside as possible for the purpose of size reductions. Two such positivelenses having strong refracting power and convex surfaces on theirobject sides and such a negative lens having a concave surface on itsimage plane side, if they are fabricated with decentration errors withrespect to their optical axes, have increased influences ondeterioration of performance. For this reason, the positive lens on theimage plane side and the negative lens should preferably be cementedtogether. When this cemented lens and the positive lens on the objectside are held in a lens holder, it is preferable that they are receivedtherein while the peripheral edges of the convex surfaces thereof abutat their peripheries or at their peripheral several spots against thelens holder.

[0041] According to a further embodiment of the present invention, thereis provided a zoom lens system characterized by comprising, in orderfrom an object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move constantly from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable duringzooming, wherein said third lens group comprises a cemented lensconsisting of a positive lens and a negative lens, said fourth lensgroup comprises one positive lens, and the following condition (10) issatisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

[0042] For zooming from the wide-angle end to the telephoto endaccording to this arrangement, the second lens group having negativerefracting power is moved from the object side to the image plane sideand the third lens group having positive refracting power is moved fromthe image plane side to the object side, so that the zooming load so farapplied on the second lens group can be assigned to the second and thirdlens groups. This in turn makes it possible to obtain the desired zoomratio and achieve size reductions without increasing the power ratio ofthe first lens group with respect to the second lens group. According tosuch an arrangement wherein the proportion of the zooming actionallocated to the third lens group is increased, it is thus possible toobtain the desired zoom ratio and achieve size reductions withoutincreasing the power ratio of the first lens group with the second lensgroup.

[0043] Reference is now made to what action and effect are obtained whenthe third lens group comprises a cemented lens consisting of a positivelens and a negative lens. When the third lens group is designed to bemovable during zooming, the load of correction of aberrationfluctuations with zooming on the third lens group increases with theneed of making more satisfactory correction for chromatic aberrations.For this reason, the third lens group is required to comprise a positivelens component and a negative lens component. If, in this case, relativedecentration occurs between the positive lens and the negative lens,there is then large deterioration of image-formation capability. In theaforesaid arrangement, the decentration between the positive lens andthe negative lens can be easily reduced by using a cemented lensconsisting of a positive lens and a negative lens in the third lensgroup. In other words, it is possible to increase the proportion of thezooming action assigned to the third lens group, make good correctionfor chromatic aberrations, and make image quality unlikely todeteriorate due to decentration.

[0044] According to the aforesaid arrangement wherein the load ofzooming so far assigned to the second lens group is allocated to thesecond and third lens groups, the load of correction of aberrations onthe fourth lens group can be successfully reduced, so that the fourthlens group can be constructed of one positive lens and, hence, thedesired image-formation capability can be obtained with size reductions.

[0045] In the aforesaid arrangement, it is preferable that at least onesurface of the positive lens forming the fourth lens group is defined byan aspherical surface.

[0046] When the fourth lens group is constructed of one positive lenstogether with one aspherical surface introduced therein, the load ofzooming can be allocated to the second and third lens groups, and thefourth lens group—whose weight is reduced accordingly—makes it possibleto achieve much better correction for aberrations, resulting in furthercost and size reductions. It is noted that the aspherical surface usedhere may be formed by a so-called glass pressing process, a (so-calledhybrid) process for applying a thin resin layer on a glass or othersubstrate, or a plastic molding process.

[0047] According to a further embodiment of the present invention, thereis provided a zoom lens system characterized by comprising, in orderfrom an object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move constantly from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable duringzooming, wherein said second lens group, and said third lens groupcomprises a cemented lens consisting of a positive lens and a negativelens, and the following condition (10) is satisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

[0048] For zooming from the wide-angle end to the telephoto endaccording to this arrangement, the second lens group having negativerefracting power is moved from the object side to the image plane sideand the third lens group having positive refracting power is moved fromthe image plane side to the object side, so that the zooming load so farapplied on the second lens group can be assigned to the second and thirdlens groups. This in turn makes it possible to obtain the desired zoomratio and achieve size reductions without increasing the power ratio ofthe first lens group with respect to the second lens group. According tosuch an arrangement wherein the proportion of the zooming actionallocated to the third lens group is increased, it is thus possible toobtain the desired zoom ratio and achieve size reductions withoutincreasing the power ratio of the first lens group with the second lensgroup.

[0049] Reference is now made to what action and effect are obtained whenthe third lens group comprises a cemented lens consisting of a positivelens and a negative lens. When the third lens group is designed to bemovable during zooming, the load of correction of aberrationfluctuations with zooming on the third lens group increases with theneed of making more satisfactory correction for chromatic aberrations.For this reason, the third lens group is required to comprise a positivelens component and a negative lens component. If, in this case, relativedecentration occurs between the positive lens and the negative lens,there is then large deterioration of image-formation capability. In theaforesaid arrangement, the decentration between the positive lens andthe negative lens can be easily reduced by using a cemented lensconsisting of a positive lens and a negative lens in the third lensgroup. In other words, it is possible to increase the proportion of thezooming action assigned to the third lens group, make good correctionfor chromatic aberrations, and make deterioration of image quality dueto decentration unlikely to occur.

[0050] Although the load applied on the second lens group is reduced,this lens group is a movable lens group during zooming. Still, a largeload is imposed on the second lens group to make correction foraberration fluctuations with zooming; it is required to makesatisfactory correction for chromatic aberrations. It is thus requiredthat the second lens group comprise at least a positive lens componentand a negative lens component. When, at this time, relative decentrationoccurs between the positive lens and the negative lens, theimage-formation capability deteriorates excessively. According to theaforesaid arrangement wherein a cemented lens consisting of a positivelens and a negative lens is introduced in the second lens group, thedecentration between the positive lens and the negative lens can beeasily reduced. It is thus possible to make deterioration of imagequality due to unlikely to occur.

[0051] According to a further embodiment of the present invention, thereis provided a zoom lens system characterized by comprising, in orderfrom an object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move constantly from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable duringzooming, wherein said third lens group comprises, in order from anobject side thereof, a positive lens and a cemented lens consisting of apositive lens and a negative lens, and the following condition (10) issatisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

[0052] For zooming from the wide-angle end to the telephoto endaccording to this arrangement, the second lens group having negativerefracting power is moved from the object side to the image plane sideand the third lens group having positive refracting power is moved fromthe image plane side to the object side, so that the zooming load so farapplied on the second lens group can be assigned to the second and thirdlens groups. This in turn makes it possible to obtain the desired zoomratio and achieve size reductions without increasing the power ratio ofthe first lens group with respect to the second lens group. According tosuch an arrangement wherein the proportion of the zooming actionallocated to the third lens group is increased, it is thus possible toobtain the desired zoom ratio and achieve size reductions withoutincreasing the power ratio of the first lens group with the second lensgroup.

[0053] The third lens group is constructed of three lenses or apositive, a positive and a negative lens in order from an object sidethereof, so that the principal points of the third lens group can begenerally located to the object side, thereby achieving further sizereductions. Here, the negative lens is needed for correction ofchromatic aberrations, and two positive lenses are needed to obtainstrong positive power and reduce the size of the third lens group itself(simplify the construction of the third lens group itself). The ++−construction of the third lens group in order from the object side alsoallows various aberrations to be well corrected with a reduced number oflenses and the principal points of the third lens group to be generallylocated on the object side, so that the principal point positions of thesecond and third lens groups can efficiently be brought close to eachother at the telephoto end, thereby achieving further size reductions ofthe zoom lens system.

[0054] According to a further embodiment of the present invention, thereis provided a zoom lens system characterized by comprising, in orderfrom an object side of said zoom lens, a first lens group havingpositive refracting power, a second lens group having negativerefracting power, a third lens group having positive refracting powerand a fourth lens group having positive refracting power, wherein aspacing between said first lens group and said second lens group, aspacing between said second lens group and said third lens group, and aspacing between said third lens group and said fourth lens group variesupon zooming, said third lens group comprises, in order from an objectside thereof, a double-convex positive lens and a cemented lensconsisting of a positive meniscus lens convex on an object side thereofand a negative meniscus lens, said fourth lens group comprises adouble-convex lens in which an object-side surface thereof has a largercurvature, and the following condition (10) is satisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

[0055] According to this arrangement wherein the third lens groupcomprises, in order from an object side thereof, a positive lens convexon an object side thereof and a cemented lens consisting of a positivemeniscus lens convex on an object side thereof and a negative meniscuslens, the principal points of the third lens group can generally belocated on the object side, so that the size of the zoom lens system canbe reduced. The cemented lens consisting of a positive meniscus lens anda negative meniscus lens is effective to reduce deterioration ofperformance due to decentration. The third lens group of suchconstruction enables the fourth lens group to be made up one singlelens. By using as the single lens a double-convex lens wherein anobject-side surface thereof has a larger curvature, it is furtherpossible to make light rays incident on an image plane nearlytelecentric and obtain the desired back focus while the number of lensesin the fourth lens group is minimized. It is thus possible to accomplishthe aforesaid another object of the present invention.

[0056] According to a further embodiment of the present invention, thereis provided a zoom lens system characterized by comprising, in orderfrom an object side of said zoom lens, a first lens group havingpositive refracting power, a second lens group having negativerefracting power, a third lens group having positive refracting powerand a fourth lens group having positive refracting power, wherein aspacing between said first lens group and said second lens group, aspacing between said second lens group and said third lens group, and aspacing between said third lens group and said fourth lens group variesupon zooming, said third lens group comprises three lenses or a singlelens and a cemented lens consisting of a positive lens and a negativelens in order from an object side thereof, said fourth lens groupcomprises one positive lens, and the following condition (10) issatisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

[0057] According to this arrangement, it is possible to achieve a zoomlens system of +−++ construction, which ensures satisfactoryimage-formation capability with a reduced number of lenses and issuitable for use on digital cameras. Here, the load of correction ofaberrations is assigned exclusively to the second and third lens groups,and so the first and fourth lens groups taking less part in correctionof aberrations can be each composed of one positive lens. According tothe construction of the second lens group taking a substantial part incorrection of aberrations wherein a single lens and a cemented lensconsisting of a negative lens and a positive lens are provided in orderfrom the object side, it is possible to reduce with a minimum number oflenses various aberrations inclusive of chromatic aberration produced atthe third lens group alone, thereby making an additional contribution tosize reductions. The cemented lens consisting of a negative lens and apositive lens, introduced in the third lens group, makes it possible toreduce deterioration of performance due to decentration.

[0058] Preferably, the power of the first lens group should bedecreased, because the amount of aberrations produced at the first lensgroup can be reduced so that the load of correction of aberrationsproduced at the first lens group on the second and third lens groups canbe reduced. Preferably, the zoom lens system according to thisembodiment should satisfy the following condition (9):

8<F ₁ /IH<20  (9)

[0059] Here F₁ is the focal length of the first lens group, and IHrepresents an image height (the length from the center of an image tothe periphery of the image or the radius of an image circle). Fallingbelow the lower limit of 8 to condition (9) is not preferable becausethe amount of aberrations produced at the first lens group becomeslarge. When the upper limit of 20 is exceeded, the power of the firstlens group becomes too weak to obtain the desired sufficient zoom ratioor achieve size reductions.

[0060] According to a further embodiment of the present invention, thereis provided a zoom lens system characterized by comprising, in orderfrom an object side of said zoom lens, a first lens group havingpositive refracting power, a second lens group having negativerefracting power, a third lens group having positive refracting powerand a fourth lens group having positive refracting power, wherein aspacing between said first lens group and said second lens group, aspacing between said second lens group and said third lens group, and aspacing between said third lens group and said fourth lens group variesupon zooming, said first lens group comprises two lenses or a positivelens and a negative lens, said second or third lens group includestherein a cemented lens consisting of at least one set of a positivelens and a negative lens, and the following condition (10) is satisfied.

2.5 min<f _(B(min))<4.8 mm  (10)

[0061] According to this arrangement wherein the first lens groupcomprises two lenses or a positive lens and a negative lens, chromaticaberration produced at the first lens group can be reduced irrespectiveof the power of the first lens group, so that the load of correction ofchromatic aberrations on the second, third, and fourth lens groups canbe relieved to reduce the overall size of the zoom lens system. Byintroducing the cemented lens consisting of a positive lens and anegative lens in the second or third lens group, it is then possible toreduce chromatic aberrations produced at lens groups other than thefirst lens group and prevent deterioration of image-formation capabilitydue to decentration, etc. It is thus possible to achieve an opticalsystem that is favorable in view of the number of lenses, fabricationcost, and size.

[0062] Preferably, the zoom lens systems according to the aforesaidembodiments of the present invention should satisfy the followingcondition (11).

2.5 mm<f _(B(max))<4.8 mm  (11)

[0063] Here f_(B(max)) is the length, as calculated on an air basis, ofthe final surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes longest in a whole zooming space.

[0064] When the lower limit of 2.5 mm to condition (11) is not reached,it is impossible to obtain any space for receiving image pickup devicepackages or filters such as IR cut filters and low-pass filters, as inthe case of condition (10). Accordingly, when these packages or filtersare incorporated in the optical system, interference or other problemsare likely to arise. When the upper limit of 4.8 mm is exceeded, on theother hand, no size reductions are achievable. This condition isimportant to conform zoom lens system size to the size of portableinformation terminals such as portable telephones and notebook PCs, inwhich the zoom lens system is incorporated.

[0065] For further size reductions, it is more preferable that

2.5 mm<f _(B(min))<4.0 mm

[0066] For further size reductions, it is more preferable that

2.5 mm<f _(B(max))<4.0 mm

[0067] Still other objects and advantages of the present invention willin part be obvious and will in part be apparent from the specification.

[0068] The present invention accordingly comprises the features ofconstruction, combinations of elements, and arrangement of parts whichwill be exemplified in the construction hereinafter set forth, and thescope of the present invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069]FIG. 1 is a sectional schematic illustrative of Example 1 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0070]FIG. 2 is a sectional schematic illustrative of Example 2 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0071]FIG. 3 is a sectional schematic illustrative of Example 3 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0072]FIG. 4 is a sectional schematic illustrative of Example 4 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0073]FIG. 5 is a sectional schematic illustrative of Example 5 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0074]FIG. 6 is a sectional schematic illustrative of Example 6 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0075]FIG. 7 is a sectional schematic illustrative of Example 7 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0076]FIG. 8 is a sectional schematic illustrative of Example 8 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0077]FIG. 9 is a sectional schematic illustrative of Example 9 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0078]FIG. 10 is a sectional schematic illustrative of Example 10 of thezoom lens system according to the present invention, as viewed at thewide-angle end.

[0079]FIG. 11 is illustrative of a holding structure for the third lensgroup in Example 5.

[0080]FIG. 12 is an aberration diagram for Example 1 at the wide-angleend.

[0081]FIG. 13 is an aberration diagram for Example 1 at the telephotoend.

[0082]FIG. 14 is a front perspective view illustrative of the appearanceof an electronic camera wherein the zoom lens system of the presentinvention is incorporated in the form of an objective optical system.

[0083]FIG. 15 is a rear perspective view illustrative of the electroniccamera wherein the zoom lens system of the present invention isincorporated in the form of an objective optical system.

[0084]FIG. 16 is a sectional view illustrative of the electronic camerawherein the zoom lens system of the present invention is incorporated inthe form of an objective optical system.

[0085]FIG. 17 is a front perspective view illustrative of an uncoveredpersonal computer wherein the zoom lens system of the present inventionis incorporated in the form of an objective optical system.

[0086]FIG. 18 is a sectional view of a phototaking optical system in thepersonal computer.

[0087]FIG. 19 is a side view of FIG. 17.

[0088] FIGS. 20(a) and 20(b) are a front and a side view illustrative ofa portable telephone wherein the zoom lens system of the presentinvention is incorporated in the form of an objective optical system,and FIG. 20(c) is a sectional view of a phototaking optical system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0089] Examples 1 to 10 of the zoom lens system according to the presentinvention are now explained.

[0090]FIGS. 1 through 10 are sectional views, as viewed at thewide-angle ends, of Examples 1 to 10 of the zoom lens system accordingto the present invention. Numerical data on each example will be set outlater. Throughout the embodiments shown in FIGS. 1 to 10, plane-parallelplates are located between the fourth lens groups G4 and image planes.These, for instance, include an image pickup device cover glass, andfilters such as an IR cut filter and a low-pass filter. Theseplane-parallel plates are omitted from the numerical data given later.

[0091] Example 1 is directed to a zoom lens system having a focal lengthof 3.643 to 10.420 mm and a field angle of 66.42° to 24°. As shown inFIG. 1, the first lens group G1 is made up of a cemented lens consistingof a negative meniscus lens convex on an object side thereof and adouble-convex lens and a positive meniscus lens convex on an object sidethereof. The second lens group G2 is made up of a negative meniscus lensconvex on an object side thereof and a cemented lens consisting of adouble-concave lens and a double-convex lens. In the rear of the secondlens group G2 there is located a stop S. The third lens group G3 is madeup of two double-convex lenses and a negative meniscus lens convex on anobject side thereof, and the fourth lens group G4 is made up of onepositive meniscus lens convex on an object side thereof. One aspehricalsurface is used for the surface located nearest to the object side inthe third lens group G3. For zooming from the wide-angle end to thetelephoto end, the first lens group G1 and the stop S remain fixed, thesecond lens group G2 moves from the object side to the image plane side,and the third and fourth lens groups G3 and G4 move from the image planeside to the object side while the space therebetween becomes wide, asindicated by arrows.

[0092] Example 2 is directed to a zoom lens system having a focal lengthof 2.924 to 8.425 mm and a field angle of 67.04° to 23.72°. As shown inFIG. 2, the first lens group G1 is made up of a cemented lens consistingof a negative meniscus lens convex on an object side thereof and apositive meniscus lens, and the second lens group G2 is made up of anegative meniscus lens convex on an object side thereof, adouble-concave lens and a positive meniscus lens convex on an objectside thereof. In the rear of the second lens group G1 there is located astop S. The third lens group G3 is made up of two double-convex lensesand a negative meniscus lens convex on an object side thereof, and thefourth lens group G4 is made up of one double-convex lens. Oneaspehrical surface is used for the surface located nearest to the objectside in the third lens group G3. For zooming from the wide-angle end tothe telephoto end, the first lens group G1 and the stop S remain fixed,the second lens group G2 moves from the object side to the image planeside, and the third and fourth lens groups G3 and G4 move from the imageplane side to the object side while the space therebetween becomes wide,as indicated by arrows.

[0093] Example 3 is directed to a zoom lens system having a focal lengthof 3.238 to 9.300 mm and a field angle of 66.82° to 23.88°. As shown inFIG. 3, the first lens group G1 is made up of a cemented lens consistingof a negative meniscus lens convex on an object side thereof and adouble-convex lens, and the second lens group G2 is made up of adouble-concave lens and a positive lens. In the rear of the second lensgroup G2 there is located a stop S. The third lens group G3 is made upof a double-convex lens, a positive meniscus lens convex on an objectside thereof and a negative meniscus lens convex on an object sidethereof, and the fourth lens group G4 is made up of one positivemeniscus lens convex on an object side thereof. Three asphericalsurfaces are used; one for the surface located nearest to the imageplane side in the second lens group G2, one for the surface locatednearest to the object side in the third lens group G3 and one for thesurface located nearest to the object side in the fourth lens group G4.For zooming from the wide-angle end to the telephoto end, the first lensgroup G1 and the stop S remain fixed, the second lens group G2 movesfrom the object side to the image plane side, and the third and fourthlens groups G3 and G4 move from the image plane side to the object sidewhile the space therebetween becomes wide, as indicated by arrows.

[0094] Example 4 is directed to a zoom lens system having a focal lengthof 3.144 to 9.070 mm and a field angle of 64.93° to 24.87°. As shown inFIG. 4, the first lens, group G1 is made up of one positive meniscuslens convex on an object side thereof, and the second lens group G2 ismade up of a negative meniscus lens convex on an object side thereof anda cemented lens consisting of a double-concave lens and a positivemeniscus lens convex on an object side thereof. In the rear of thesecond lens group G2 there is located a stop S. The third lens group G3is made up of a double-convex lens and a cemented lens consisting of apositive meniscus lens convex on an object side thereof and a negativemeniscus lens, and the fourth lens group G4 is made up of onedouble-convex lens. Two aspherical surfaces are used; one for thesurface located nearest to the object side in the third lens group G3and another for the surface located nearest to the object side in thefourth lens group G4. For zooming from the wide-angle end to thetelephoto end, the first lens group G1 and the stop S remain fixed, thesecond lens group G2 moves from the object side to the image plane side,and the third and fourth lens groups G3 and G4 move from the image planeside to the object side while the space therebetween becomes wide, asindicated by arrows.

[0095] Example 5 is directed to a zoom lens system having a focal lengthof 3.578 to 10.193 mm and a field angle of 68.30° to 24.54°. As shown inFIG. 5, the first lens group G1 is made up of a negative meniscus lensconvex on an object side thereof and a positive meniscus lens convex onan object side thereof, and the second lens group G2 is made up of anegative meniscus lens convex on an object side thereof and a cementedlens consisting of a double-concave lens and a positive meniscus lensconvex on an object side thereof. In the rear of the second lens groupG2 there is located a stop S. The third lens group G3 is made up of adouble-convex lens and a cemented lens consisting of a positive meniscuslens convex on an object side thereof and a negative meniscus lensconvex on an object side thereof, and the fourth lens group G4 is madeup of one double-convex lens. Three aspherical surfaces are used; onefor the surface located nearest to the image plane side in the secondlens group G2, one for the surface located nearest to the object side inthe third lens group G3 and one for the surface located nearest to theobject side in the fourth lens group G4. For zooming from the wide-angleend to the telephoto end, the first lens group G1 and the stop S remainfixed, the second lens group G2 moves from the object side to the imageplane side, and the third and fourth lens groups G3 and G4 move from theimage plane side to the object side while the space therebetween becomeswide, as indicated by arrows.

[0096] In Example 5, it is noted that both the object-side positive lensL₃₁ and cemented lens L₃₂ in the third lens group G3 are held while theperipheral edges of the convex surfaces thereof abut peripherally or atseveral spots against a lens holder 1, so that decentration errorslikely to have an influence on performance can be reduced.

[0097] Example 6 is directed to a zoom lens system having a focal lengthof 2.478 to 7.162 mm and a field angle of 67.32° to 25.95°. As shown inFIG. 6, the first lens group G1 is made up of one plano-convex lens, andthe second lens group G2 is made up of a negative meniscus lens convexon an object side thereof and a cemented lens consisting of adouble-concave lens and a positive meniscus lens convex on an objectside thereof. In the rear of the second lens group G2 there is located astop S. The third lens group G3 is made up of a double-convex lens and acemented lens consisting of a positive meniscus lens convex on an objectside thereof and a negative meniscus lens convex on an object sidethereof, and the fourth lens group G4 is made up of one double-convexlens. Two aspherical surfaces are used; one for the surface locatednearest to the object side in the third lens group G3 and another forthe surface located nearest to the object side in the fourth lens groupG4. For zooming from the wide-angle end to the telephoto end, the firstlens group G1 and the stop S remain fixed, the second lens group G2moves from the object side to the image plane side, and the third andfourth lens groups G3 and G4 move from the image plane side to theobject side while the space therebetween becomes wide, as indicated byarrows.

[0098] Example 7 is directed to a zoom lens system having a focal lengthof 2.976 to 8.549 mm and a field angle of 67.68° to 26.08°. As shown inFIG. 7, the first lens group G1 is made up of one plano-convex lens, andthe second lens group G2 is made up of a negative meniscus lens convexon an object side thereof and a cemented lens consisting of adouble-concave lens and a positive meniscus lens convex on an objectside thereof. In the rear of the second lens group G2 there is located astop S. The third lens group G3 is made up of a double-convex lens and acemented lens consisting of a positive meniscus lens convex on an objectside thereof and a negative meniscus lens convex on an object sidethereof, and the fourth lens group G4 is made up of a double-convex lensand a negative meniscus lens convex on an image plane side thereof. Oneaspehrical surface is used for the surface located nearest to the objectside in the third lens group G3. For zooming from the wide-angle end tothe telephoto end, the first lens group G1 and the stop S remain fixed,the second lens group G2 moves from the object side to the image planeside, and the third and fourth lens groups G3 and G4 move from the imageplane side to the object side while the space therebetween becomes wide,as indicated by arrows.

[0099] Example 8 is directed to a zoom lens system having a focal lengthof 4.093 to 11.875 mm and a field angle of 67.80° to 26.68°. As shown inFIG. 8, the first lens group G1 is made up of a negative meniscus lensconvex on an object side thereof and a positive meniscus lens convex onan object side thereof, and the second lens group G2 is made up of anegative meniscus lens convex on an object side thereof and a cementedlens consisting of a double-concave lens and a positive meniscus lensconvex on an object side thereof. In the rear of the second lens groupG2 there is located a stop S. The third lens group G3 is made up of adouble-convex lens and a cemented lens consisting of a double-convexlens and a double-concave lens, and the fourth lens group is made up ofone double-convex lens. Two aspherical surfaces are used; one for thesurface located nearest to the object side in the third lens group G3and another for the surface located nearest to the object side in thefourth lens group G4. For zooming from the wide-angle end to thetelephoto end, the first lens group G1 and the stop S remain fixed, thesecond lens group G2 moves from the object side to the image plane side,and the third and fourth lens groups G3 and G4 move from the image planeside to the object side while the space therebetween becomes wide, asindicated by arrows.

[0100] Example 9 is directed to a zoom lens system having a focal lengthof 3.281 to 9.500 mm and a field angle of 67.69° to 26.08°. As shown inFIG. 9, the first lens group G1 is made up of a cemented lens consistingof a negative meniscus lens convex on an object side thereof and apositive meniscus lens convex on an object side thereof, and the secondlens group G2 is made up of a negative meniscus lens convex on an objectside thereof and a cemented lens consisting of a double-concave lens anda positive meniscus lens convex on an object side thereof. In the rearof the second lens group G2 there is located a stop S. The third lensgroup G3 is made up of a double-convex lens and a cemented lensconsisting of a double-convex lens and a double-concave lens, and thefourth lens group G4 is made up of one double-convex lens. Twoaspherical surfaces are used; one for the surface located nearest to theobject side in the third lens group G3 and another for the surfacelocated nearest to the object side in the fourth lens group G4. Forzooming from the wide-angle end to the telephoto end, the first lensgroup G1 and the stop S remain fixed, the second lens group G2 movesfrom the object side to the image plane side, and the third and fourthlens groups G3 and G4 move from the image plane side to the object sidewhile the space therebetween becomes wide, as indicated by arrows.

[0101] Example 10 is directed to a zoom lens system having a focallength of 3.634 to 10.687 mm and a field angle of 68.52° to 26.08°. Asshown in FIG. 10, the first lens group G1 is made up of a cemented lensconsisting of a negative meniscus lens convex on an object side thereofand a positive meniscus lens convex on an object side thereof, and thesecond lens group G2 is made up of a negative meniscus lens convex on anobject side thereof and a cemented lens consisting of a double-concavelens and a positive meniscus lens convex on an object side thereof. Inthe rear of the second lens group G2 there is located a stop S. Thethird lens group G3 is made up of a double-convex lens and a cementedlens consisting of a double-convex lens and a double-concave lens, andthe fourth lens group G4 is made up of one double-convex lens. Twoaspherical surfaces are used; one for the surface located nearest to theobject side in the third lens group G3 and another for the surfacelocated nearest to the object side in the fourth lens group G4. Forzooming from the wide-angle end to the telephoto end, the first lensgroup G1 and the stop S remain fixed, the second lens group G2 movesfrom the object side to the image plane side, and the third and fourthlens groups G3 and G4 move from the image plane side to the object sidewhile the space therebetween becomes wide, as indicated by arrows.

[0102] Set out below are numerical data on each example, with the unitof length being mm. Symbols used hereinafter but not hereinbefore havethe following meanings.

[0103] f: the focal length of the zoom lens system,

[0104] F_(NO): an F-number,

[0105] f_(B): a back focus as calculated on an air basis,

[0106] r₁, r₂, . . . : the radius of curvature of each lens surface,

[0107] d₁, d₂, . . . : the separation between adjacent lens surfaces,

[0108] n_(d1), n_(d2), . . . : the d-line refractive index of each lens,and

[0109] ν_(d1), ν_(d2), . . . : the Abbe number of each lens.

[0110] Here let x denote an optical axis provided that the direction ofpropagation of light is positive and y represent a directionperpendicular to the optical axis. Then, aspherical shape is given by

x=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y¹⁰ +A ₁₂ y ¹²

[0111] where r is the paraxial radius of curvature, K is a conicalcoefficient, and A₄, A₆, A₈, A₁₀ and A₁₂ are the fourth, sixth, eighth,tenth and twelfth aspherical coefficients, respectively. Example 1 f =3.643 ˜ 6.310 ˜ 10.420 F_(NO) = 2.79 ˜ 3.22 ˜ 4.11 f _(B) = 3.43 ˜ 3.73˜ 4.11 r₁ = 123.446 d₁ = 0.79 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ =26.028 d₂ = 2.63 n_(d2) = 1.48749 ν_(d2) = 70.23 r₃ = −37.648 d₃ = 0.12r₄ = 9.745 d₄ = 2.16 n_(d3) = 1.69680 ν_(d3) = 55.53 r₅ = 41.109 d₅ =(Variable) r₆ = 49.306 d₆ = 0.56 n_(d4) = 1.77250 ν_(d4) = 49.60 r₇ =3.668 d₇ = 1.97 r₈ = −6.439 d₈ = 0.56 n_(d5) = 1.48749 ν_(d5) = 70.21 r₉= 7.824 d₉ = 1.19 n_(d6) = 1.84666 ν_(d6) = 23.78 r₁₀ = −92.465 d₁₀ =(Variable) r₁₁ = ∞ (Stop) d₁₁ = (Variable) r₁₂ = 7.726 (Aspheric) d₁₂ =1.29 n_(d7) = 1.58913 ν_(d7) = 61.18 r₁₃ = −15.280 d₁₃ = 0.10 r₁₄ =5.743 d₁₄ = 1.73 n_(d8) = 1.72916 ν_(d8) = 54.68 r₁₅ = −8.215 d₁₅ = 0.20r₁₆ = 17.851 d₁₆ = 0.46 n_(d9) = 1.84666 ν_(d9) = 23.78 r₁₇ = 2.797 d₁₇= (Variable) r₁₈ = 6.406 d₁₈ = 1.07 n_(d10) = 1.72916 ν_(d10) = 54.68r₁₉ = 21.794 Zooming Spaces f 3.643 6.310 10.420 d₅ 0.64 2.95 4.22 d₁₀4.43 2.13 0.86 d₁₁ 3.24 2.25 0.62 d₁₇ 1.61 2.30 3.55 AsphericalCoefficients 12th surface K = −0.218 A₄ = −3.12469 × 10⁻³ A₆ = −2.00580× 10⁻⁴ A₈ = 2.58848 × 10⁻⁵ A₁₀ = −3.98934 × 10⁻⁶ | F₂ / F₃ | = 0.714 F₃/ F₄ = 0.539 | β_(2T) | = 0.897 | L₃ / L₂ | = 0.73 (F_(3.4W)) / IH =2.44 F₁ / IH = 6.97 IH = 2.25 Example 2 f = 2.924 ˜ 5.049 ˜ 8.425 F_(NO)= 2.78 ˜ 3.39 ˜ 4.22 f_(B) = 2.69 ˜ 3.00 ˜ 4.18 r₁ = 9.603 d₁ = 0.64n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 6.804 d₂ = 2.74 n_(d2) = 1.60311ν_(d2) = 60.64 r₃ = 121.247 d₃ = (Variable) r₄ = 21.867 d₄ = 0.41 n_(d3)= 1.65160 ν_(d3) = 58.55 r₅ = 2.740 d₅ = 1.87 r₆ = −17.627 d₆ = 0.37n_(d4) = 1.56384 ν_(d4) = 60.67 r₇ = 10.992 d₇ = −0.01 r₈ = 4.352 d₈ =0.93 n_(d5) = 1.80518 ν_(d5) = 25.42 r₉ = 6.985 d₉ = (Variable) r₁₀ = ∞(Stop) d₁₀ = (Variable) r₁₁ = 6.533 (Aspheric) d₁₁ = 1.96 n_(d6) =1.67790 ν_(d6) = 55.34 r₁₂ = −6.275 d₁₂ = 0.45 r₁₃ = 6.079 d₁₃ = 1.25n_(d7) = 1.60311 ν_(d7) = 60.64 r₁₄ = −9.868 d₁₄ = 0.07 r₁₅ = 25.676 d₁₅= 0.37 n_(d8) = 1.84666 ν_(d8) = 23.78 r₁₆ = 2.938 d₁₆ = (Variable) r₁₇= 7.544 d₁₇ = 0.91 n_(d9) = 1.58913 ν_(d9) = 61.14 r₁₈ = −46.010 ZoomingSpaces f 2.924 5.049 8.425 d₃ 0.36 2.53 4.14 d₉ 4.46 2.29 0.69 d₁₀ 2.851.70 0.50 d₁₆ 1.02 1.85 1.88 Aspherical Coefficients 11th surface K =−0.218 A₄ = −4.79076 × 10⁻³ A₆ = 7.18792 × 10⁻⁴ A₈ = −2.84416 × 10⁻⁴ A₁₀= 4.21243 × 10⁻⁵ | F₂ /F₃ | = 0.837 F₃ / F₄ = 0.475 | β_(2T) | = 0.501 |L₃ / L₂ | = 0.62 (F_(3.4W)) / IH = 2.58 F₁ / IH = 10.99 IH = 1.8 Example3 f = 3.238 ˜ 5.605 ˜ 9.300 F_(NO) = 2.79 ˜ 3.35 ˜ 4.33 f_(B) = 3.05 ˜3.45 ˜ 4.42 r₁ = 11.229 d₁ = 0.71 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ =8.678 d₂ = 1.82 n_(d2) = 1.60311 ν_(d2) = 60.64 r₃ = −4524.933 d₃ =(Variable) r₄ = −44.964 d₄ = 0.49 n_(d3) = 1.77250 ν_(d3) = 49.60 r₅ =2.859 d₅ = 1.07 r₆ = 10.754 d₆ = 1.04 n_(d4) = 1.80518 ν_(d4) = 25.42 r₇= ∞ (Aspheric) d₇ = (Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ = 4.318(Aspheric) d₉ = 1.55 n_(d5) = 1.58913 ν_(d5) = 61.18 r₁₀ = −13.012 d₁₀ =0.09 r₁₁ = 4.720 d₁₁ = 1.16 n_(d6) = 1.72916 ν_(d6) = 54.68 r₁₂ = 30.878d₁₂ = 0.09 r₁₃ = 8.260 d₁₃ = 0.41 n_(d7) = 1.84666 ν_(d7) = 23.78 r₁₄ =2.400 d₁₄ = (Variable) r₁₅ = 5.989 (Aspheric) d₁₅ = 1.03 n_(d8) =1.58913 ν_(d8) = 61.14 r₁₆ = 666.490 Zooming Spaces f 3.238 5.605 9.300d₃ 0.68 3.22 4.76 d₇ 4.85 2.31 0.76 d₈ 3.32 2.13 0.55 d₁₄ 1.22 2.01 2.63Aspherical Coefficients 7th surface K = 0.000 A₄ = −2.85671 × 10⁻³ A₆ =−5.00585 × 10⁻⁶ A₈ = −4.55482 × 10⁻⁵ A₁₀ = 1.15287 × 10⁻⁶ 9th surface K= −0.218 A₄ = −2.53050 × 10⁻³ A₆ = −3.22409 × 10⁻⁵ A₈ = 1.05400 × 10⁻⁵A₁₀ = −1.24302 × 10⁻⁶ 15th surface K = 0.000 A₄ = −1.11182 × 10⁻³ A₆ =2.52212 × 10⁻⁴ A₈ = −6.19443 × 10⁻⁵ A₁₀ = 1.11195 × 10⁻⁵ | F₂ / F₃ | =0.866 F₃ / F₄ = 0.591 | β_(2T) | = 0.575 | L₃ / L₂ | = 0.68 (F_(3.4W)) /IH = 2.52 F₁ / IH = 10.06 IH = 2.0 Example 4 f = 3.144 ˜ 5.518 ˜ 9.070F_(NO) = 2.78 ˜ 3.34 ˜ 4.35 f_(B) = 2.85 ˜ 3.29 ˜ 4.40 r₁ = 9.466 d₁ =2.06 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = 325.991 d₂ = (Variable) r₃ =19.366 d₃ = 0.48 n_(d2) = 1.84666 ν_(d2) = 23.78 r₄ = 3.135 d₄ = 1.51 r₅= −7.920 d₅ = 0.46 n_(d3) = 1.48749 ν_(d3) = 70.23 r₆ = 4.420 d₆ = 1.49n_(d4) = 1.84666 ν_(d4) = 23.78 r₇ = 241.864 d₇ = (Variable) r₈ = ∞(Stop) d₈ = (Variable) r₉ = 4.925 (Aspheric) d₉ = 1.91 n_(d5) = 1.56384ν_(d5) = 60.67 r₁₀ = −9.657 d₁₀ = 0.07 r₁₁ = 4.433 d₁₁ = 1.64 n_(d6) =1.77250 ν_(d6) = 49.60 r₁₂ = 147.741 d₁₂ = 0.40 n_(d7) = 1.84666 ν_(d7)= 23.78 r₁₃ = 2.588 d₁₃ = (Variable) r₁₄ = 5.552 (Aspheric) d₁₄ = 1.40n_(d8) = 1.56384 ν_(d8) = 60.67 r₁₅ = −26.965 Zooming Spaces f 3.1445.518 9.070 d₂ 0.56 3.27 4.59 d₇ 4.78 2.27 0.74 d₈ 3.73 2.40 0.53 d₁₃1.29 2.16 2.95 Aspherical Coefficients 9th surface K = −0.218 A₄ =−1.70776 × 10⁻³ A₆ = 3.80242 × 10⁻⁶ A₈ = 6.65158 × 10⁻⁷ A₁₀ = −2.95559 ×10⁻⁸ 14th surface K = 0.000 A₄ = −5.91729 × 10⁻⁴ A₆ = −4.46239 × 10⁻⁵ A₈= 1.89881 × 10⁻⁵ A₁₀ = 0 | F₂ / F₃ | = 0.779 F₃ / F₄ = 0.794 | β_(2T) |= 0.586 | L₃ / L₂ | = 0.792 (F_(3.4W)) / IH = 2.71 F₁ / IH = 9.98 IH =2.0 Example 5 f = 3.538 ˜ 6.063 ˜ 10.193 F_(NO) = 1.99 ˜ 2.27 ˜ 2.71f_(B) = 3.52 ˜ 4.13 ˜ 5.01 r₁ = 11.700 d₁, = 0.75 n_(d1) = 1.80518ν_(d1) = 25.42 r₂ = 8.376 d₂ = 0.22 r₃ = 8.983 d₃ = 3.12 n_(d2) =1.69680 ν_(d2) = 55.53 r₄ = 1994.627 d₄ = (Variable) r₅ − 272.962 d₅ =0.51 n_(d3) = 1.77250 ν_(d3) = 49.60 r₆ = 3.607 d₆ = 1.90 r₇ = −67.501d₇ = 0.51 n_(d4) = 1.48749 ν_(d4) = 70.23 r₈ = 6.854 d₈ = 1.49 n_(d5) =1.72250 ν_(d5) = 29.20 r₉ = 47.648 (Aspheric) d₉ = (Variable) r₁₀ = ∞(Stop) d₁₀ = (Variable) r₁₁ = 5.926 (Aspheric) d₁₁ = 1.93 n_(d6) =1.66910 ν_(d6) = 55.40 r₁₂ = −19.572 d₁₂ = 0.09 r₁₃ = 4.844 d₁₃ = 1.64n_(d7) = 1.67790 ν_(d7) = 55.34 r₁₄ = 51.623 d₁₄ = 0.45 n_(d8) = 1.84666ν_(d8) = 23.78 r₁₅ = 3.195 d₁₅ = (Variable) r₁₆ = 6.105 (Aspheric) d₁₆ =1.82 n_(d9) = 1.66910 ν_(d9) = 55.40 r₁₇ = −24.730 Zooming Spaces f3.538 6.063 10.193 d₄ 0.49 3.25 5.27 d₉ 5.60 2.83 0.84 d₁₀ 3.20 2.060.60 d₁₅ 1.45 1.97 2.55 Aspherical Coefficients 9th surface K = 0.000 A₄= −9.99655 × 10⁻⁴ A₆ = 3.86110 × 10⁻⁵ A₈ = −1.20035 × 10⁻⁵ A₁₀ = 6.80269× 10⁻⁷ 11th surface K = −0.218 A₄ = −6.82101 × 10⁻⁴ A₆ = −1.21088 × 10⁻⁵A₈ = 3.20658 × 10⁻⁶ A₁₀ = −2.47777 × 10⁻⁷ 16th surface K = 0.000 A₄ =−9.45299 × 10⁻⁴ A₆ = 2.83288 × 10⁻⁵ A₈ = −2.50040 × 10⁻⁷ A₁₀ = 0 | F₂ /F₃ | = 0.628 F₃ / F₄ = 1.088 | β_(2T) | = 0.760 | L₃ / L₂ | = 0.54(F_(3.4W)) / IH = 2.67 F₁ / IH = 8.73 IH = 2.25 Example 6 f = 2.478 ˜4.226 ˜ 7.162 F_(NO) = 2.03 ˜ 2.36 ˜ 2.91 f_(B) = 2.83 ˜ 3.44 ˜ 4.66 r₁= 13.758 d₁ = 1.55 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = ∞ d₂ =(Variable) r₃ = 8.156 d₃ = 0.47 n_(d2) = 1.84666 ν_(d2) = 23.78 r₄ =3.020 d₄ = 2.04 r₅ = −10.317 d₅ = 0.38 n_(d3) = 1.48749 ν_(d3) = 70.23r₆ = 3.905 d₆ = 1.69 n_(d4) = 1.84666 ν_(d4) = 23.78 r₇ = 15.206 d₇ =(Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ = 6.594 (Aspheric) d₉ = 1.28n_(d5) = 1.58913 ν_(d5) = 61.30 r₁₀ = −13.376 d₁₀ = 0.08 n₁₁ = 3.521 d₁₁= 1.63 n_(d6) = 1.77250 ν_(d6) = 49.60 r₁₂ = 32.979 d₁₂ = 0.34 n_(d7) =1.84666 ν_(d7) = 23.78 r₁₃ = 2.478 d₁₃ = (Variable) r₁₄ = 5.082(Aspheric) d₁₄ = 1.23 n_(d8) = 1.58913 ν_(d8) = 61.30 r₁₅ = −11.553Zooming Spaces f 2.478 4.226 7.162 d₂ 0.38 3.62 5.92 d₇ 6.07 2.83 0.56d₈ 3.25 2.05 0.56 d₁₃ 1.30 1.88 2.14 Aspherical Coefficients 9th surfaceK = 0.000 A₄ = −8.83776 × 10⁻⁴ A₆ = −1.79814 × 10⁻⁴ A₈ = 6.59986 × 10⁻⁵A₁₀ = −8.05802 × 10⁻⁶ A₁₂ = 5.90942 × 10⁻⁸ 14th surface K = 0.000 A₄ =−1.88373 × 10⁻³ A₆ = −1.31653 × 10⁻⁴ A₈ = 3.07847 × 10⁻⁴ A₁₀ = −1.33087× 10⁻⁴ A₁₂ = 1.81422 × 10⁻⁵ | F₂ / F₃ | = 0.77 F₃ / F₄ = 1.12 | β_(2T) |= 0.35 | L₃ / L₂ | = 0.48 (F_(3.4W)) / IH = 3.06 F₁ / IH = 17.10 IH =1.5 Example 7 f = 2.976 ˜ 5.065 ˜ 8.549 F_(NO) = 2.64 ˜ 3.01 ˜ 3.85f_(B) = 2.91 ˜ 3.47 ˜ 4.54 r₁ = 12.405 d₁ = 1.98 n_(d1) = 1.48749 ν_(d1)= 70.23 r₂ = ∞ d₂ = (Variable) r₃ = 15.574 d₃ = 0.45 n_(d2) = 1.84666ν_(d2) = 23.78 r₄ = 3.425 d₄ = 1.88 r₅ = −11.707 d₅ = 0.43 n_(d3) =1.48749 ν_(d3) = 70.23 r₆ = 4.402 d₆ = 1.51 n_(d4) = 1.84666 ν_(d4) =23.78 r₇ = 34.871 d₇ = (Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ =4.077 (Aspheric) d₉ = 1.55 n_(d5) = 1.58913 ν_(d5) = 61.28 r₁₀ = −12.990d₁₀ = 0.09 r₁₁ = 6.194 d₁₁ = 1.40 n_(d6) = 1.77250 ν_(d6) = 49.60 r₁₂ =36.559 d₁₂ = 0.41 n_(d7) = 1.84666 ν_(d7) = 23.78 r₁₃ = 2.869 d₁₃ =(Variable) r₁₄ = 7.598 d₁₄ = 1.14 n_(d8) = 1.80400 ν_(d8) = 46.57 r₁₅ =−10.188 d₁₅ = 0.41 r₁₆ = −6.224 d₁₆ = 0.45 n_(d9) = 1.84666 ν_(d9) =23.78 r₁₇ = −9.384 Zooming Spaces f 2.976 5.065 8.549 d₂ 0.45 3.82 5.95d₇ 6.18 2.81 0.68 d₈ 3.61 2.46 0.59 d₁₃ 1.07 1.67 2.49 AsphericalCoefficients 9th surface K = 0.000 A₄ = −2.68388 × 10⁻³ A₆ = 8.86517 ×10⁻⁵ A₈ = −6.80012 × 10⁻⁵ A₁₀ = 1.65400 × 10⁻⁵ A₁₂ = −1.50666 × 10⁻⁶ |F₂ / F₃ | = 0.76 F₃ /F₄ = 1.09 | β_(2T) | = 0.50 | L₃ / L₂ | − 0.,55(F_(3.4W)) / IH = 2.79 F₁ / IH = 12.85 IH = 1.8 Example 8 f = 4.093 ˜7.041 ˜ 11.875 F_(NO) = 2.02 ˜ 2.33 ˜ 2.80 f_(B) = 4.53 ˜ 5.42 ˜ 6.90 r₁= 18.108 d₁ = 0.94 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 12.307 d₂ = 0.14r₃ = 12.753 d₃ = 3.10 n_(d2) = 1.77250 ν_(d2) = 49.60 r₄ = 122.843 d₄ =(Variable) r₅ = 26.311 d₅ = 0.63 n_(d3) = 1.77250 ν_(d3) = 49.60 r₆ =4.431 d₆ = 2.94 r₇ = −26.320 d₇ = 0.59 n_(d4) = 1.57250 ν_(d4) = 57.74r₈ = 4.874 d₈ = 2.27 n_(d5) = 1.80100 ν_(d5) = 34.97 r₉ = 32.145 d₉ =(Variable) r₁₀ = ∞ (Stop) d₁₀ = (Variable) r₁₁ = 8.399 (Aspheric) d₁₁ =1.78 n_(d6) = 1.58913 ν_(d6) = 61.30 r₁₂ = −20.918 d₁₂ = 0.13 r₁₃ =10.353 d₁₃ = 3.13 n_(d7) = 1.77250 ν_(d7) = 49.60 r₁₄ = −5.691 d₁₄ =0.56 n_(d8) = 1.68893 ν_(d8) = 31.07 r₁₅ = 4.778 d₁₅ = (Variable) r₁₆ =8.696 (Aspheric) d₁₆ = 3.13 n_(d9) = 1.58913 ν_(d9) = 61.30 r₁₇ =−16.508 Zooming Spaces f 4.093 7.041 11.875 d₄ 0.63 4.63 7.56 d₉ 7.873.87 0.94 d₁₀ 4.43 2.75 0.84 d₁₅ 1.26 2.05 2.48 Aspherical Coefficients11th surface K = 0.000 A₄ = −4.74324 × 10⁻⁴ A₆ = −2.42146 × 10⁻⁵ A₈ =2.49585 × 10⁻⁶ A₁₀ = −1.17216 × 10⁻⁷ 16th surface K = 0.000 A₄ =−6.18094 × 10⁻⁴ A₆ = 7.96643 × 10⁻⁵ A₈ = −1.16593 × 10⁻⁵ A₁₀ = 6.32501 ×10⁻⁷ | F₂ / F₃ | = 0.64 F₃ / F₄ = 1.07 | β_(2T) | = 0.56 | L₃ / L₂ | =0.52 (F_(3.4W)) / IH = 2.81 F₁ / IH = 10.96 IH = 2.5 Example 9 f = 3.281˜ 5.633 ˜ 9.500 F_(NO) = 2.03 ˜ 2.41 ˜ 2.98 f_(B) = 2.98 ˜ 3.50 ˜ 4.60r₁ = 13.782 d₁ = 0.90 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 11.125 d₂ =2.64 n_(d2) = 1.69680 ν_(d2) = 55.53 r₃ = 73.145 d₃ = (Variable) r₄ =16.578 d₄ = 0.60 n_(d3) = 1.84666 ν_(d3) = 23.78 r₅ = 3.821 d₅ = 2.97 r₆= −16.432 d₆ = 0.47 n_(d4) = 1.58913 ν_(d4) = 61.14 r₇ = 4.721 d₇ = 2.50n_(d5) = 1.84666 ν_(d5) = 23.78 r₈ = 36.357 d₈ = (Variable) r₉ = ∞(Stop) d₉ = (Variable) r₁₀ = 6.997 (Aspheric) d₁₀ = 2.32 n_(d6) =1.58913 ν_(d6) = 61.30 r₁₁ = −13.157 d₁₁ = 0.10 r₁₂ = 5.948 d₁₂ = 2.50n_(d7) = 1.77250 ν_(d7) = 49.60 r₁₃ = −9.882 d₁₃ = 0.45 n_(d8) = 1.80518ν_(d8) = 25.42 r₁₄ = 3.525 d₁₄ = (Variable) r₁₅ = 6.328 (Aspheric) d₁₅ =2.50 n_(d9) = 1.58913 ν_(d9) = 61.30 r₁₆ = −18.262 Zooming Spaces f3.281 5.633 9.500 d₃ 0.50 3.55 5.78 d₈ 6.03 2.99 0.75 d₉ 3.91 2.44 0.68d₁₄ 0.64 1.59 2.27 Aspherical Coefficients 10th surface K = 0.000 A₄ =−6.74025 × 10⁻⁴ A₆ = −3.39527 × 10⁻⁵ A₈ = 6.17490 × 10⁻⁶ A₁₀ = −3.69154× 10⁻⁷ 15th surface K = 0.000 A₄ = −1.22978 × 10⁻³ A₆ = 2.57259 × 10⁻⁴A₈ = −5.94053 × 10⁻⁵ A₁₀ = 5.10256 × 10⁻⁶ | F₂ / F₃ | = 0.72 F₃ / F₄ =0.96 | β_(2T) | = 0.55 | L₃ / L₂ | = 0.61 (F_(3.4W)) / IH = 2.73 F₁ / IH= 11.41 IH = 2.0 Example 10 f = 3.634 ˜ 6.338 ˜ 10.687 F_(NO) = 2.03 ˜2.36 ˜ 2.86 f_(B) = 4.06 ˜ 5.03 ˜ 6.69 r₁ = 25.537 d₁ = 0.84 n_(d1) =1.84666 ν_(d1) = 23.78 r₂ = 17.128 d₂ = 1.92 n_(d2) = 1.77250 ν_(d2) =49.60 r₃ = 41.101 d₃ = 0.11 r₄ = 17.177 d₄ = 2.25 n_(d3) = 1.60311ν_(d3) = 60.64 r₅ = 64.686 d₅ = (Variable) r₆ = 21.366 d₆ = 0.56 n_(d4)= 1.80610 ν_(d4) = 40.92 r₇ = 4.013 d₇ = 2.78 r₈ = −19.517 d₈ = 0.53n_(d5) = 1.59551 ν_(d5) = 39.24 r₉ − 4.450 d₉ = 2.10 n_(d6) = 1.80518ν_(d6) = 25.42 r₁₀ = 34.830 d₁₀ = (Variable) r₁₁ = ∞ (Stop) d₁₁ =(Variable) r₁₂ = 11.333 (Aspheric) d₁₂ = 2.15 n_(d7) = 1.58913 ν_(d7) =61.30 r₁₃ = −15.421 d₁₃ = 0.11 r₁₄ = 6.624 d₁₄ = 2.81 n_(d8) = 1.77250ν_(d8) = 49.60 r₁₅ = −9.336 d₁₅ = 0.51 n_(d9) = 1.74077 ν_(d9) = 27.79r₁₆ = 4.319 d₁₆ = (Variable) r₁₇ = 8.127 (Aspheric) d₁₇ = 2.81 n₁₀ =1.58913 ν_(d10) = 61.30 r₁₈ = −13.550 Zooming Spaces f 3.634 6.33810.687 d₅ 0.56 4.10 6.61 d₁₀ 6.89 3.35 0.84 d₁₁ 4.43 2.65 0.76 d₁₆ 1.662.46 2.70 Aspherical Coefficients 12th surface K = 0.000 A₄ = −2.72290 ×10⁻⁴ A₆ = −2.67214 × 10⁻⁵ A₈ = 3.52082 × 10⁻⁶ A₁₀ = −1.72643 × 10⁻⁷ 17thsurface K = 0.000 A₄ −6.98015 × 10⁻⁴ A₆ = 8.08033 × 10⁻⁵ A₈ = −1.17442 ×10⁻⁵ A₁₀ = 6.68163 × 10⁻⁷ | F₂ / F₃ | = 0.59 F₃ /F₄ = 1.08 | β_(2T) | =0.55 | L₃ / L₂ | = 0.61 (F_(3.4W)) / IH = 2.96 F₁ / IH = 11.19 IH = 2.25

[0112]FIGS. 12 and 13 are aberration diagrams for Example 1 of thepresent zoom lens system at the wide-angle and telephoto ends,respectively, upon focused on an object point at infinity. In thesedrawings, (a), (b), (c), (d) and (e) represent spherical aberrations,astigmatism, distortion, chromatic aberration of magnification and coma,respectively. It is noted that ω stands for a half field angle.

[0113] The zoom lens system according to the present invention may beused on various image pickup systems using electronic image pickupdevices such as CCD or CMOS sensors, as embodied below.

[0114] An electronic cameral wherein the zoom lens system of the presentinvention is incorporated in the form of an objective optical system isshown in FIGS. 14 to 16. FIG. 14 is a front perspective viewillustrative of the appearance of an electronic camera 200, and FIG. 15is a rear perspective view illustrative of the electronic camera 200.FIG. 16 is a sectional view illustrative of the construction of theelectronic camera 200. As shown in FIGS. 14 to 16, the electronic camera200 comprises a phototaking optical system 202 including a phototakingoptical path 201, a finder optical system 204 including a finder opticalpath 203, a shutter 205, a flash 206 and a liquid crystal displaymonitor 207. Upon pressing down the shutter 205 located on the upperportion of the camera 200, phototaking occurs through an objective lenssystem 12 comprising the instant zoom lens system (roughly shown)located as a phototaking objective optical system. An object imageformed through the phototaking optical system is then formed on theimage pickup plane of an image pickup device chip 62 such as a CCD viaan IR (infrared rays) cut filter 80.

[0115] The object image sensed by image pickup device chip 62 isdisplayed as an electronic image on the liquid crystal display monitor207 located on the back side of the camera via processing means 208electrically connected to a terminal 66. This processing means 208 mayalso control recording means 209 for recording the object imagephototaken through the image pickup device chip 62 in the form ofelectronic information. It is here noted that the recording means 209may be provided as a memory mounted on the processing means 208 or inthe form of a device electrically connected to the processing means 208to electronically write the information into a magnetic recording mediumsuch as a floppy disk or smart media.

[0116] Further, the finder optical system 204 having a finder opticalpath 203 comprises a finder objective optical system 210, a Porro prism211 for erecting the object image formed through the finder objectiveoptical system 210 and an eyepiece 212 for guiding the object image tothe eyeball E of an observer. The Porro prism 211 is divided into afront and a rear block with an object image-forming surface locatedbetween them. The Porro prism 211 comprises four reflecting surfaces toerect the object image formed through the finder objective opticalsystem 204.

[0117] To reduce the number of parts and achieve compactness and costreductions, the finder optical system 204 may be removed from the camera200. In this case, the observer carries out phototaking while looking atthe liquid crystal monitor 207.

[0118] Shown in FIGS. 17 to 19 is a personal computer that is oneexample of the information processor in which the zoom lens system ofthe invention is incorporated in the form of an objective opticalsystem. FIG. 17 is a front perspective views of an uncovered personalcomputer 300, FIG. 18 is a sectional view of a phototaking opticalsystem 303 mounted on the personal computer 300, and FIG. 19 is a sideview of FIG. 17. As depicted in FIGS. 17 to 19, the personal computer300 comprises a key board 301 for allowing an operator to enterinformation therein from outside, information processing and recordingmeans (not shown), a monitor 302 for displaying the information to theoperator and a phototaking optical system 303 for phototaking an imageof the operator per se and images of operator's surroundings. Themonitor 302 used herein may be a transmission type liquid crystaldisplay device designed to be illuminated by a backlight (not shown)from the back side, a reflection type liquid crystal display devicedesigned to display images by reflecting light from the front side, aCRT display or the like. As shown, the phototaking optical system 303 isbuilt in a right upper portion of monitor 302. However, it is to beunderstood that the phototaking optical system 303 may be positionedsomewhere on the periphery of monitor 302 or keyboard 301.

[0119] The phototaking optical system 303 includes on a phototakingoptical path 304 an objective lens system 12 comprising the zoom lenssystem of the invention (roughly shown) and an image pickup device chip62 for receiving an image. These are built in the personal computer 300.

[0120] An object image sensed by the image pickup device chip 62 isentered from a terminal 66 in the processing means in the personalcomputer 300, and displayed as an electronic image on the monitor 302.Shown in FIG. 17 as an example is a phototaken image 305 of theoperator. It is possible to display the image 305, etc. on a personalcomputer at the other end on a remote place via an internet or telephoneline.

[0121] Illustrated in FIG. 20 is a telephone handset that is one exampleof the information processor in which the zoom lens system of theinvention is built in the form of a phototaking optical system,especially a convenient-to-carry portable telephone handset. FIG. 20(a)is a front view of a portable telephone handset 400, FIG. 20(b) is aside view of handset 400 and FIG. 20(c) is a sectional view of aphototaking optical system 405. As depicted in FIGS. 20(a) to 20(c), thetelephone handset 400 comprises a microphone portion 401 for entering anoperators voice therein as information, a speaker portion 402 forproducing a voice of a person on the other end, an input dial 403allowing the operator to enter information therein, a monitor 404 fordisplaying phototaken images of the operator and the person on the otherend and information such as telephone numbers, a phototaking opticalsystem 405, an antenna 406 for transmitting and receiving communicationwaves and a processing means (not shown) for processing imageinformation, communication information, input signals, etc. The monitor404 used herein is a liquid crystal display device. The arrangement ofthese parts is not necessarily limited to that illustrated. Thephototaking optical system 405 includes on a phototaking optical path407 an objective lens system 12 comprising the zoom lens system (roughlyillustrated) of the invention and an image pickup device chip 62 forreceiving an object image. These are built in the telephone handset 400.

[0122] The object image sensed by the image pickup device chip 62 isentered from a terminal 66 in a processing means (not shown), anddisplayed as an electronic image on the monitor 404 and/or a monitor onthe other end. To transmit an image to a person on the other end, theprocessing means includes a signal processing function of convertinginformation about the object image received at the image pickup elementchip 62 to transmittable signals.

[0123] According to the present invention as explained above, it is thuspossible to achieve a compact yet low-cost zoom lens system, andespecially a zoom lens system suitable for use on portable informationterminals of small size.

What we claim is:
 1. A zoom lens system comprising, in order from anobject side of said zoom lens system, a first lens group having positiverefracting power and designed to be fixed during zooming, a second lensgroup having negative refracting power and designed to move from theobject side to an image plane side of the zoom lens system for zoomingfrom a wide-angle end to a telephoto end of said zoom lens system, athird lens group having positive refracting power and designed to movefrom the image plane side to the object side for zooming from thewide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied: 0.5<|F ₂ /F₃|<1.2  (1)2.5 mm<f _(B(min))<4.8 mm  (10) where F_(i) is a focal lengthof an i-th lens group and f_(B(min)) is a length, as calculated on anair basis, of a final surface of a lens having power in said zoom lenssystem to an image plane of said zoom lens system, representing a figureat which said zoom lens system becomes shortest in a whole zoomingspace.
 2. A zoom lens system comprising, in order from an object side ofsaid zoom lens system, a first lens group having positive refractingpower and designed to be fixed during zooming, a second lens grouphaving negative refracting power and designed to move from the objectside to an image plane side of said zoom lens system for zooming from awide-angle end to a telephoto end of said zoom lens system, a third lensgroup having positive refracting power and designed to move from theimage plane side to the object side for zooming from the wide-angle endto the telephoto end, and a fourth lens group having positive refractingpower and designed to be movable for zooming, wherein the followingconditions are satisfied: 0.49<|L ₃ /L ₂|<1  (2)2.5 mm<f _(B(min))<4.8mm  (10) where L_(i) is an amount of movement of an i-th lens group fromthe wide-angle end to the telephoto end and f_(B(min)) is a length, ascalculated on an air basis, of a final surface of a lens having power insaid zoom lens system to an image plane of said zoom lens system,representing a figure at which said zoom lens system becomes shortest ina whole zooming space.
 3. A zoom lens system comprising, in order froman object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move from the object side to the image plane side for zooming fromthe wide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied: 2<( F_(3.4W))/IH<3.3  (3)2.5 mm<f _(B(min))<4.8 mm  (10) where (F_(3.4W)) isa composite focal length of the third and forth lens groups at thewide-angle end, IH is a radius of an image circle, and f_(B(min)) is alength, as calculated on an air basis, of a final surface of a lenshaving power in said zoom lens system to an image plane of said zoomlens system, representing a figure at which said zoom lens systembecomes shortest in a whole zooming space.
 4. A zoom lens systemcomprising, in order from an object side of said zoom lens system, afirst lens group having positive refracting power, a second lens grouphaving negative refracting power and designed to move from the objectside to an image plane side of said zoom lens system for zooming awide-angle end to a telephoto end of said zoom lens system, a third lensgroup having positive refracting power and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein said third lens group comprises, in order from an object sidethereof, a positive lens component convex on an object side thereof anda cemented lens consisting of a positive lens element convex on anobject side thereof and a negative lens element concave on an imageplane side thereof, and both the object-side positive lens component andthe cemented lens in said third lens group are held in a lens barrelwhile the object-side convex surfaces thereof abut peripherally or atperipheral several spots against said lens barrel, and the followingcondition is satisfied: 2.5 mm<f _(B(min))<4.8 mm  (10) where f_(B(min))is a length, as calculated on an air basis, of a final surface of a lenshaving power in said zoom lens system to an image plane of said zoomlens system, representing a figure at which said zoom lens systembecomes shortest in a whole zooming space.
 5. A zoom lens systemcomprising, in order from an object side of said zoom lens system, afirst lens group having positive refracting power and designed to befixed during zooming, a second lens group having negative refractingpower and designed to move from the object side to an image plane sideof the zoom lens system for zooming from a wide-angle end to a telephotoend of said zoom lens system, a third lens group having positiverefracting power and designed to move from the image plane side to theobject side for zooming from the wide-angle end to the telephoto end,and a fourth lens group having positive refracting power and designed tobe movable for zooming, wherein the following conditions are satisfied:0.5<|F ₂ /F ₃|<1.2  (1)0.49<|L ₃ /L ₂|<1  (2)2.5 mm<f _(B(min))<4.8mm  (10) where F_(i) is a focal length of an i-th lens group, L_(i) isan amount of an i-th lens group from the wide-angle end to the telephotoend, and f_(B(min)) is a length, as calculated on an air basis, of afinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.
 6. Azoom lens system comprising, in order from an object side of said zoomlens system, a first lens group having positive refracting power anddesigned to be fixed during zooming, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming from a wide-angle end toa telephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move from the image plane sideto the object side for zooming from the wide-angle end to the telephotoend, and a fourth lens group having positive refracting power anddesigned to be movable for zooming, wherein the following conditions aresatisfied: 0.5<|F ₂ /F ₃|<1.2  (1)2<(F _(3.4W))/IH<3.3  (3)2.5 mm<f_(B(min))<4.8 mm  (10) where F_(i) is a focal length of an i-th lensgroup, (F_(3.4W)) is a composite focal length of the third and forthlens groups at the wide-angle end, IH is a radius of an image circle,and f_(B(min)) is a length, as calculated on an air basis, of a finalsurface of a lens having power in said zoom lens system to an imageplane of said zoom lens system, representing a figure at which said zoomlens system becomes shortest in a whole zooming space.
 7. A zoom lenssystem comprising, in order from an object side of said zoom lenssystem, a first lens group having positive refracting power and designedto be fixed during zooming, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming from a wide-angle end toa telephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move from the image plane sideto the object side for zooming from the wide-angle end to the telephotoend, and a fourth lens group having positive refracting power anddesigned to be movable for zooming, wherein the following conditions aresatisfied: 0.49<|L ₃ /L ₂|<1  (2)2<(F _(3.4W))/IH<3.3  (3)2.5 mm<f_(B(min))<4.8 mm  (10) where L_(i) is an amount of movement of an i-thlens group, (F_(3.4W)) is a composite focal length of the third andforth lens groups at the wide-angle end, IH is a radius of an imagecircle, and f_(B(min)) is a length, as calculated on an air basis, of afinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.
 8. Azoom lens system comprising, in order from an object side of said zoomlens system, a first lens group having positive refracting power anddesigned to be fixed during zooming, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming from a wide-angle end toa telephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move from the image plane sideto the object side for zooming from the wide-angle end to the telephotoend, and a fourth lens group having positive refracting power anddesigned to be movable for zooming, wherein the following conditions aresatisfied: 0.5<|F ₂ /F ₃|<1.2  (1)0.49<|L ₃ /L ₂|<1  (2)2<(F_(3.4W))/IH|<3.3  (3)2.5 mm<f _(B(min))<4.8 mm  (10) where F_(i) is afocal length of an i-th lens group, L_(i) is an amount of movement of ani-th lens group, (F_(3.4W)) is a composite focal length of the third andforth lens groups at the wide-angle end, IH is a radius of an imagecircle, and f_(B(min)) is a length, as calculated on an air basis, of afinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.
 9. Thezoom lens system according to any one of claims 1, 2, 3, and 5 to 8,which further satisfies the following condition: 0.6<|F ₂ /F ₃|<1  (4)where F_(i) is the focal length of an i-th lens group.
 10. The zoom lenssystem according to any one of claims 1, 2, 3, and 5 to 8, wherein saidfourth lens group is moved in an optical axis direction for focusing.11. The zoom lens system according to any one of claims 1, 2, 3, and 5to 8, which further satisfies the following condition: 0.3<|F ₃ /F₄|<0.8  (5) where F_(i) is the focal length of an i-th lens group. 12.The zoom lens system according to any one of claims 1, 2, 3, and 5 to 8,which further satisfies the following condition: 0.4<|β_(2T)|<1  (6)where β_(2T) is a transverse magnification of the second lens group. 13.The zoom lens system according to any one of claims 1, 2, 3, and 5 to 8,wherein said fourth lens group consists of one positive lens element.14. The zoom lens system according to any one of claims 1, 2, 3, and 5to 8, wherein said third lens group consists of three lenses elements ora positive lens element, a positive lens element and a negative lenselement in order from an object side thereof.
 15. The zoom lens systemaccording to any one of claims 1, 2, 3, and 5 to 8, wherein at least onesurface in said third lens group is defined by an aspherical surface.16. The zoom lens system according to any one of claims 1, 2, 3, and 5to 8, wherein at least one surface in said fourth lens group is definedby an aspherical surface.
 17. The zoom lens system according to any oneof claims 1, 2, 3, and 5 to 8, wherein at least one surface in saidsecond lens group is defined by an aspherical surface.
 18. A zoom lenssystem comprising, in order from an object side of said zoom lenssystem, a first lens group having positive refracting power and designedto be fixed during zooming, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming from a wide-angle end toa telephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move from the image plane sideto the object side for zooming from the wide-angle end to the telephotoend, and a fourth lens group having positive refracting power anddesigned to be movable for zooming, wherein said first lens groupconsists of one positive lens element, a lens element located nearest tothe object side in said second lens group is defined by a negative lenselement, and the following conditions are satisfied: ν₂₁<40  (7)2.5 mm<f_(B(min))<4.8 mm  (10) where ν₂₁ is an Abbe's number of said negativelens element located nearest to the object side in said second lensgroup, and f_(B(min)) is a length, as calculated on an air basis, of afinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.
 19. Thezoom lens system according to claim 18, which satisfies the followingcondition: ν₂₁<35  (8)
 20. The zoom lens system according to any one ofclaims 1, 2, 3, and 5 to 8, wherein a lens element located nearest tothe object side in said second lens group is defined by a negative lenselement, and the following condition is satisfied: ν₂₁<40  (7) where ν₂₁is an Abbe's number of said negative lens element located nearest to theobject side in said second lens group.
 21. The zoom lens systemaccording to claim 20, which satisfies the following condition:ν₂₁<35  (8) where ν₂₁ is the Abbe's number of said negative lens elementlocated nearest to the object side in said second lens group.
 22. Thezoom lens system according to any one of claims 1, 2, 3, 5 to 8, 18 and19, wherein said third lens group comprises, in order from an objectside thereof, a positive lens component convex on an object side thereofand a cemented lens consisting of a positive lens element convex on anobject side thereof and a negative lens element concave on an image sidethereof, and said cemented lens and said positive lens on the objectside are held in a lens barrel while the peripheral edges of the convexsurfaces thereof abut peripherally or at peripheral several spotsagainst the lens barrel.
 23. A zoom lens system comprising, in orderfrom an object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move constantly from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable duringzooming, wherein said third lens group comprises a cemented lensconsisting of a positive lens element and a negative lens element, saidfourth lens group consists of one positive lens element, and thefollowing condition (10) is satisfied: 2.5 mm<f _(B(min))<4.8 mm  (10)where f_(B(min)) is a length, as calculated on an air basis, of a finalsurface of a lens having power in said zoom lens system to an imageplane of said zoom lens system, representing a figure at which said zoomlens system becomes shortest in a whole zooming space.
 24. The zoom lenssystem according to claim 23, wherein at least one surface of saidpositive lens in said fourth lens group is defined by an asphericalsurface.
 25. A zoom lens system comprising, in order from an object sideof said zoom lens system, a first lens group having positive refractingpower and designed to be fixed during zooming, a second lens grouphaving negative refracting power and designed to move from the objectside to an image plane side of said zoom lens system for zooming from awide-angle end to a telephoto end of said zoom lens system, a third lensgroup having positive refracting power and designed to move constantlyfrom the image plane side to the object side for zooming from thewide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable during zooming,wherein said second lens group, and said third lens group comprises acemented lens consisting of a positive lens element and a negative lenselement, and the following condition (10) is satisfied: 2.5 mm<f_(B(min))<4.8 mm  (10) where f_(B(min)) is a length, as calculated on anair basis, of a final surface of a lens having power in said zoom lenssystem to an image plane of said zoom lens system, representing a figureat which said zoom lens system becomes shortest in a whole zoomingspace.
 26. A zoom lens system comprising, in order from an object sideof said zoom lens system, a first lens group having positive refractingpower and designed to be fixed during zooming, a second lens grouphaving negative refracting power and designed to move from the objectside to an image plane side of said zoom lens system for zooming from awide-angle end to a telephoto end of said zoom lens system, a third lensgroup having positive refracting power and designed to move constantlyfrom the image plane side to the object side for zooming from thewide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable during zooming,wherein said third lens group comprises, in order from an object sidethereof, a positive lens component and a cemented lens consisting of apositive lens element and a negative lens element, and the followingcondition (10) is satisfied: 2.5 mm<f _(B(min))<4.8 mm  (10) wheref_(B(min)) is a length, as calculated on an air basis, of a finalsurface of a lens having power in said zoom lens system to an imageplane of said zoom lens system, representing a figure at which said zoomlens system becomes shortest in a whole zooming space.
 27. A zoom lenssystem comprising, in order from an object side of said zoom lens, afirst lens group having positive refracting power, a second lens grouphaving negative refracting power, a third lens group having positiverefracting power and a fourth lens group having positive refractingpower, wherein a spacing between said first lens group and said secondlens group, a spacing between said second lens group and said third lensgroup, and a spacing between said third lens group and said fourth lensgroup varies upon zooming, said third lens group comprises, in orderfrom an object side thereof, a double-convex positive lens component anda cemented lens consisting of a positive meniscus lens element convex onan object side thereof and a negative meniscus lens element, said fourthlens group comprises a double-convex lens element in which anobject-side surface thereof has a larger curvature, and the followingcondition (10) is satisfied: 2.5 mm<f _(B(min))<4.8 mm  (10) wheref_(B(min)) is a length, as calculated on an air basis, of a finalsurface of a lens having power in said zoom lens system to an imageplane of said zoom lens system, representing a figure at which said zoomlens system becomes shortest in a whole zooming space.
 28. A zoom lenssystem comprising, in order from an object side of said zoom lens, afirst lens group having positive refracting power, a second lens grouphaving negative refracting power, a third lens group having positiverefracting power and a fourth lens group having positive refractingpower, wherein a spacing between said first lens group and said secondlens group, a spacing between said second lens group and said third lensgroup, and a spacing between said third lens group and said fourth lensgroup varies upon zooming, said first lens group consists of onepositive lens component, said second lens group comprises three lenselements or one single lens element and a cemented lens consisting of anegative lens element and a positive lens element in order from anobject side thereof, said third lens group comprises three lens elementsor a single lens element and a cemented lens consisting of a positivelens element and a negative lens element in order from an object sidethereof, said fourth lens group consists of one positive lens element,and the following condition (10) is satisfied: 2.5 mm<f _(B(min))<4.8mm  (10) where f_(B(min)) is a length, as calculated on an air basis, ofa final surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.
 29. Azoom lens system comprising, in order from an object side of said zoomlens, a first lens group having positive refracting power, a second lensgroup having negative refracting power, a third lens group havingpositive refracting power and a fourth lens group having positiverefracting power, wherein a spacing between said first lens group andsaid second lens group, a spacing between said second lens group andsaid third lens group, and a spacing between said third lens group andsaid fourth lens group varies upon zooming, said first lens groupcomprises two lens elements or a positive lens element and a negativelens element, said second or third lens group includes therein acemented lens component consisting of at least one set of a positivelens element and a negative lens element, and the following condition(10) is satisfied: 2.5 mm<f _(B(min))<4.8 mm  (10) where f_(B(min)) is alength, as calculated on an air basis, of a final surface of a lenshaving power in said zoom lens system to an image plane of said zoomlens system, representing a figure at which said zoom lens systembecomes shortest in a whole zooming space.
 30. A zoom lens systemcomprising, in order from an object side of said zoom lens system, afirst lens group having positive refracting power and designed to befixed during zooming, a second lens group having negative refractingpower and designed to move from the object side to an image plane sideof said zoom lens system for zooming from a wide-angle end to atelephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move constantly from the imageplane side to the object side for zooming from the wide-angle end to thetelephoto end, and a fourth lens group consists of one lens element,having positive refracting power and designed to be movable duringzooming, wherein said second lens group, and said third lens groupcomprises a cement lens component consisting of a positive lens elementand a negative lens element, and said third lens group or said fourthlens group includes therein at least one aspherical surface.
 31. A zoomlens system comprising, in order from an object side of said zoom lens,a first lens group having positive refracting power, a second lens grouphaving negative refracting power, a third lens group having positiverefracting power and a fourth lens group having positive refractingpower, wherein a spacing between said first lens group and said secondlens group, a spacing between said second lens group and said third lensgroup, and a spacing between said third lens group and said fourth lensgroup varies upon zooming, said first lens group consists of onepositive lens element, said second lens group comprises three lenselements or a single lens element and a cemented lens consisting of anegative lens element and a positive lens element in order from anobject side thereof, said third lens group comprises three lens elementsor a single lens element and a cemented lens consisting of a positivelens element and a negative lens element, and said fourth lens elementconsists of one positive lens element, with at least one asphericalsurface introduced in said third lens group or said fourth lens group.32. The zoom lens system according to any one of claims 1 to 8, 18, 23and 25 to 31, which further satisfies the following condition: 2.5 mm<f_(B(max))<4.8 mm  (11) where f_(B(max)) is a length, as calculated on anair basis, of a final surface of a lens having power in said zoom lenssystem to an image plane of said zoom lens system, representing a figureat which said zoom lens system becomes longest in a whole zooming space.33. An image pickup system including an objective optical systemcomprising a zoom lens system as recited in any one of claims 1 to 8,18, 23 and 25 to 31, and an electronic image pickup device located on animage side of said zoom lens system.